
Take the lid off the KBS-835RP mouse and you see plenty of discrete components on the top circuit board. It looks positively, um,
classic, compared with the surface-mount, multi-layer-board, super-integrated designs that the bigger names are using in their mouses these days.
Practically, there's not much reason to be worried about a mouse with a forest of discrete components inside, instead of a smaller number of fancier parts. There are more things that can be mis-soldered or otherwise messed up in the manufacturing process when you've got more parts, so the chance of a dead-on-arrival mouse is higher. But if the thing works in the first place, it should keep working perfectly well.
Older-style construction also, of course, means older-style components, in this case at least. That explains the A4 mouse's susceptibility to skipping when you move it quickly, and it also explains the simple two minute sleep timer.